Methods of displaying a stereoscopic image include a method using polarizing spectacles and a method not using polarizing spectacles. The method using the polarizing spectacles is not widely used in stereoscopic image display apparatuses because of inconvenience resulting from the ware of spectacles and dangerousness of opthalmology diseases. The method not using the polarizing spectacles is classified into a lenticular method, a holographic method, and a parallax barrier method. Since the lenticular method and the holographic method have complicated structures and require high cost, they are used for only particular applications. The parallax barrier method has been most actively studied, developed, and commercialized.
The principle of the parallax barrier method was suggested in the early 20th century, but development of stereoscopic image display apparatuses using the parallax barrier method was regularized since flat panel display apparatuses such as liquid crystal display apparatuses, plasma display panels, and organic EL display apparatuses appeared. These days, rear type parallax-barrier stereoscopic image display apparatuses are supplied to the market. The rear type parallax-barrier stereoscopic image display apparatus means a stereoscopic image display apparatus having a structure in which a parallax barrier is disposed in the front of an image display panel.
The past rear type parallax-barrier stereoscopic image display apparatus has problems with low brightness, complicated manufacturing processes, high cost, and the like.
In order to solve the problems of the past rear type parallax-barrier stereoscopic image display apparatuses, development of front type parallax-barrier stereoscopic image display apparatuses has been attempted. However, the front type parallax-barrier stereoscopic image display apparatuses have a problem with a large visible distance (distance where a stereoscopic image is visible). For this reason, the front type parallax-barrier stereoscopic image display apparatuses were not commercialized, in spite of their merits of simple manufacturing processes and high brightness. The inventor of the present invention first suggests a front type parallax-barrier stereoscopic image display apparatus which can be commercialized. In other words, the front type parallax-barrier stereoscopic image display apparatus was not known in the art hitherto. However, the past trials of the inventor are called a prior art for the purpose of convenient explanation.
Hereinafter, problems of the past front type parallax-barrier stereoscopic image display apparatus are described with reference to the drawings.
FIG. 1 is a sectional view schematically illustrating a general 2D image liquid crystal display (LCD) panel.
A 2D image LCD panel 10 includes a first substrate 12 in which a rear polarizing film 11 is stacked on the rear surface thereof and a first switching element layer 13 is stacked on the front surface thereof and a second substrate 16 in which a color filter layer 15 is stacked on the rear surface thereof and a front polarizing film 18 is stacked on the front surface thereof. Here, a liquid crystal layer 14 is interposed between the first switching layer 13 and the color filter layer 15.
A thin film transistor (TFT) LCD panel can be used as the 2D image LCD panel 10. In this case, first switching elements of the first switching element layer 13 are TFTs. The structure and operations of the TFT LCD panel are known widely in the art and thus are described in brief.
The rear polarizing film 11 serves to polarize white light emitted from a backlight (not shown). The first and second substrates 12 and 16 are made of glass. The first substrate 12 serves as a base layer of the first switching element layer 13 and a pixel electrode layer (not shown). The TFTs are arranged in a matrix in the first switching element layer 13. An image (2D image) is displayed by driving the TFTs in accordance with an image signal. Although not shown, the pixel electrode layer made of ITO or the like is disposed under the first switching element layer 13.
The second substrate 16 serves as a base layer for forming the color filter layer 15 and the like and serves to mechanically protect the liquid crystal from external impacts. The second substrate 16 also serves to prevent oxygen and moisture from permeating the liquid crystal from the outside. Accordingly, the second substrate is made of a thick glass material with a thickness of 0.5 to 0.7 mm.
In the color filter layer 15 formed in the back of the second substrate 16, RGB color filters are arranged in a predetermined pattern.
Although not shown in the figures, a common electrode layer made of ITO or the like is disposed under the color filter layer 15. By applying a voltage between the pixel electrode layer and the common electrode layer through a wire 17, the liquid crystal molecules are aligned and an image is displayed by turning on or off the individual switching elements of the first switching element layer 13.
As described above, a first liquid crystal layer 14 made of liquid crystal is interposed between the first switching element layer 13 and the color filter layer 15, that is, between the first switching element layer 13 and the common electrode layer. Although not shown, an alignment layer is provided to initially align the liquid crystal. Light passing through the first liquid crystal layer 14 has a predetermined color by means of the RGB color filters.
With this configuration, a 2D image is displayed on the 2D image display panel 10. On the other hand, the 2D image is divided into and displayed as a left-eye image and a right-eye image for use in the stereoscopic image display apparatus. Next, a general parallax barrier LCD panel is described with reference to FIG. 2.
FIG. 2 is a sectional view schematically illustrating a general parallax-barrier LCD panel.
Referring to FIG. 2, the parallax-barrier LCD panel 20 includes a third substrate in which a rear polarizing film 21 is stacked at least on the rear surface thereof and a transparent electrode layer 23 is stacked on the front surface thereof and a protective film 25. Here, a second liquid crystal layer 24 is interposed between the transparent electrode layer 23 and the protective film 25. On the other hand, a front polarizing film 28 is stacked on the protective film 25.
A plurality of transparent electrodes are arranged in a band shape in the transparent electrode layer 23. Similarly, a plurality of counter electrodes are arranged in the counter electrode layer so as to be opposed to the plurality of transparent electrodes. The liquid crystal molecules of the second liquid crystal layer 24 are aligned depending on a voltage applied between the transparent electrodes and the counter electrodes through a wire 27. Light incident from the TFT LCD panel is blocked or transmitted depending on the alignment of the liquid crystal molecules. Accordingly, the liquid crystal layer serves as a parallax barrier.
Such a band-shaped member having a light blocking/transmitting function is called a parallax barrier. The parallax barrier allow an observer to view a stereoscopic image by allowing the left-eye image and the right-eye image displayed on the 2D image LCD panel 10 to be incident on the left eye and the right eye, respectively.
The parallax-barrier LCD panel 20 can be embodied as an LCD panel employing TN (Twisted Nematic) liquid crystal. Alternatively, the parallax-barrier LCD panel 20 may employ STN (Super-Twisted Nematic) liquid crystal or FTN (Film Compensated super twisted Nematic) liquid crystal.
Here, the protective film 25 is formed of a thick layer so as to protect the liquid crystal layer and to endure external impacts. Typically, the thickness of the protective film 25 is in the range of 0.55 to 1.1 mm.
FIG. 3 is a sectional view schematically illustrating a known stereoscopic image display apparatus.
In the past stereoscopic image display apparatus, the parallax-barrier LCD panel 20 is attached to the front surface of the 2D image LCD panel 10. The stereoscopic image display apparatus having such a structure is called a front type parallax-barrier stereoscopic image display apparatus.
Referring to FIG. 3, the known stereoscopic image display apparatus can be formed by bonding the front surface (front polarizing film 18) of the 2D image LCD panel 10 shown in FIG. 1 and the rear surface (rear polarizing film 21) of the parallax-barrier LCD panel 20 shown in FIG. 2 to each other. However, since the front polarizing film 18 and the rear polarizing film 21 perform the same operation, one thereof can be omitted. The polarizing film is shown as an intermediate polarizing film 18′ in FIG. 3.
Now, a visible distance of the known stereoscopic image display apparatus having the above-mentioned structure will be described.
In FIG. 3, a distance e between an image and the parallax barrier corresponds to a distance from the first liquid crystal layer 14 to the second liquid crystal layer 24. As shown in the figure, the color filter layer 15, the second substrate 16, the intermediate polarizing film 18′, the third substrate, and the transparent electrode layer 23 are interposed between the first liquid crystal layer 14 and the second liquid crystal layer 24. Here, since the color filter layer 15 is a very thin film (for example, chrome-deposited film) deposited on the second substrate, the thickness of the color filter layer 15 need not be considered in calculating the distance e between the image and the parallax barrier. Similarly, since the ITO layer, etc. formed on the protective film are very thin, they are collectively called a protective layer. At the time of calculating the distance e between the image and the parallax barrier, it is assumed that the thickness of the color filter layer 15 is included in the thickness of the second substrate 16.
In a stereoscopic image display apparatus for a monitor, typically, the second substrate 16 has a thickness of about 0.7 mm, the intermediate polarizing film 18′ has a thickness of about 0.3 mm, and the third substrate 22 has a thickness of about 0.7 mm. The total thickness is about 1.7 mm. In a stereoscopic image display apparatus for a mobile terminal, typically, the second substrate 16 has a thickness of about 0.5 mm, the intermediate polarizing film 18′ has a thickness of 0.1 to 0.3 mm, and the third substrate 22 has a thickness of about 0.5 mm. The total thickness is about 1.3 mm. Accordingly, the distance e between the image and the parallax barrier cannot be smaller than 1.3 mm.
An observer can recognize a stereoscopic image by placing both eyes at points on which the stereoscopic image is focused. A distance between the points at which the stereoscopic image is focused is defined as a visible distance L.
The visible distance L is determined based on the distance e between the image and the parallax barrier, an inter-eye distance E, and a pixel width P, and is expressed by Expression 1.L˜e(E/P)  (1)
Here, the inter-eye distance E is a distance between a left eye and a right eye, which varies by persons. An average inter-eye distance is about 6.5 cm. The pixel width P is a distance between pixels of an image display apparatus and is reversely proportional to the visible distance L as can be seen from Expression 1. The decrease in pixel width increases the resolution of an image but increases the visible distance. That is, the pixel width has a trade-off relation with the visible distance. In general, an image display apparatus for a monitor has a pixel width of about 100 μm and an image display apparatus for a personal mobile terminal has a pixel width of about 60 μm.
When the distance e between the image and the parallax barrier is substituted into Expression 1, the visible distance of the stereoscopic image display apparatus for a monitor is about 1.1 m and the visible distance of the stereoscopic image display apparatus for a mobile terminal is about 1.3 m. In this way, the front type parallax-barrier stereoscopic image display apparatus has a visible distance of about 1.2 m.
“That the visible distance is 1.2 m means that an observer can recognize a stereoscopic image with a distance of 1.2 m from the image display apparatus.
When the front type parallax-barrier stereoscopic image display apparatus is applied to a TV set, an observer is sufficiently spaced apart from the screen. Accordingly, the visible distance of 1.2 m causes no problem.
However, when the front type parallax-barrier stereoscopic image display apparatus is applied to a computer monitor, the visible distance of 1.2 m causes a serious problem. For example, when a gamer (observer) play a 3D game while viewing a computer monitor, the gamer should input commands by the use of a keyboard or a joy stick while viewing the screen. Since a person's average arm length is generally 70 cm or less, the gamer cannot play the game at the same time as recognizing the stereoscopic image.
When the front type parallax-barrier stereoscopic image display apparatus is applied to a mobile terminal such as a mobile phone or a PDA, the visible distance of 1.2 m also causes a serious problem. That is, it is not possible to enjoy a stereoscopic game service or confirm stereoscopic image information at the same time of recognizing a stereoscopic image by the use of a mobile terminal. Since the screen of the mobile terminal is small, it is not possible to recognize an image by employing the front type parallax-barrier stereoscopic image display apparatus.
The visible distance L required for the mobile terminal is in the range of 30 to 40 cm. Accordingly, even when a diamond zone (which is described later) of 40 to 90 cm of a mobile terminal is considered, it is not possible to view a desired stereoscopic image by the use of the known front type parallax-barrier stereoscopic image display apparatus.